The invention relates to non-contact temperature measurements of a substrate, and more particularly to probes for making such measurements during thermal processing.
Many semiconductor device manufacturing processes require strict control over the process temperatures to increase device performance and yield as well as to ensure process repeatability. To avoid damage to a substrate and undesirable process variations, precise temperature monitoring of the substrate is needed.
One method for determining substrate temperature uses the principles of pyrometry. Pyrometers, or devices based on pyrometry, exploit the general property that objects emit radiation with a particular spectral content and intensity that is characteristic of their temperature. By measuring the emitted radiation, the object's temperature can be determined. In systems that incorporate pyrometers, a reflector is positioned near the substrate to create a virtual blackbody cavity between the reflector and the substrate. Additionally, a temperature probe is used to sample radiation in the cavity through an aperture in the reflector. The sampled intensity is passed to the pyrometer where it is converted to temperature information. Further, to increase the precision of the temperature monitoring process, the emitted radiation intensity can be monitored via a plurality of temperature probes and pyrometers which monitor the temperature of localized regions of the substrate and perform appropriate conversions to obtain temperature information. Temperature readings from various probes can be used for real-time control of heating elements in processing a substrate.
Such a control scheme may be used in process chambers providing independent heating control over various portions of a substrate. For example, some process chambers include a plurality of heating elements, such as lamps, positioned over the substrate to be heated. Depending on the local temperature of the substrate, the power to the individual lamps may be varied to provide temperature uniformity across the entire substrate.
Rapid thermal processing (RTP) is an example of a fabrication process using such a plurality of heating elements. RTP is used for several different fabrication processes, including rapid thermal annealing (RTA), rapid thermal cleaning (RTC), rapid thermal chemical vapor deposition (RTCVD), rapid thermal oxidation (RTO), and rapid thermal nitridation (RTN). In the particular application of complementary metal-oxide-semiconductor (CMOS) gate dielectric formation by RTO or RTN, thickness, growth temperature and uniformity of the gate dielectrics are critical parameters that influence device performance and fabrication yield. Currently, CMOS devices are being made with dielectric layers that are only 60-80 angstroms (.ANG.) thick and for which thickness uniformity must be held within .+-.2 .ANG.. This level of uniformity requires that temperature variations across the substrate during high temperature processing cannot exceed a few degrees Celsius (.degree. C.).
The wafer itself often cannot tolerate even small temperature differentials during high temperature processing. If the temperature differential is allowed to rise above, for example, 1-2.degree. C./cm at 1200.degree. C., the resulting stress is likely to cause slip in the silicon crystal. The resulting slip planes will destroy any devices through which they pass. To achieve that level of temperature uniformity, reliable real-time, multi-point temperature measurements for closed-loop temperature control are often used.
One problem with temperature probes is that they pick-up not only the temperature of the substrate, but also the temperature of an edge position of a ring, for example, supporting the substrate. The temperature gradient or differential between the support ring and the substrate may undesirably cause inaccurate temperature measurements during processing of the substrate.